Chlorine is tricker and less 'forgiving' in a spa than three step bromine. Most people do bromine worng but when it's done right it's actually very easy. Chlorine requires daiily atttention but is much less expensive.
If you have a ozonator on the spa I would go with bromine. Ozone and chlorine don't play well together. Ozone and chlorine do.
Ozone destroys chlorine and vice versa. On the other hand ozone reactivates bromine by oxidizing bromide in the water into active bromine sanitizer. This is because of the differences in chlorine and bromine chemistry. Chlorine also reactivates bromine btw. This is why chorine can be used to 'shock' or oxidize a bromine spa.
Shocking a bromine spa serves a different purpose than shocking a chlorine one--you want to oxidize your bromide reserve in the water back into active bromine sanitizer, not destrly the bromamines that are formed since they, unlike chloramines, are effective sanitizers.